The invention described herein pertains generally to a dimensionally stable, one-component at least semi-rigid, essentially closed cell, polyurethane foam, which cures upon reaction with moisture with relatively low expansion and concomitant low pressure build, in confined spaces.
Polyurethanes in general are thermoplastic polymers, which can be made thermosetting, produced by the condensation reaction of a polyisocyanate and a hydroxyl-containing material, e.g., a polyol derived from propylene oxide. The basic polymer unit may be generically shown as follows.
R1NCO+R2OHxe2x86x92R1NHCOOR2
Polyurethanes have applications as fibers, coatings, elastomers, or foams. This invention relates to foams. Both flexible and rigid foams are available with density ranging from 0.5 to more than 60 pounds per cubic foot and thermal conductivities as low as 0.11 BTU in/ft3 h xc2x0 F. Polyurethane foams are good insulators and can be derived from polyethers such as polypropylene glycol which is reacted with a diisocyanate in the presence of some water and a catalyst, e.g., amines, tin soaps, organic tin compounds. As the polymer forms, the water reacts with the isocyanate groups to cause crosslinking and chain extension, and also produces carbon dioxide which causes foaming. In some cases, a volatile material such as a blowing agent is added separately.
Polyurethane foams are produced by the reaction of a polyol, containing hydroxyl groups (OH), and a polyisocyanate having isocyanate groups (xe2x80x94Nxe2x95x90Cxe2x95x90O), in the presence of a catalyst, a blowing (or foaming agent) and optionally a surfactant and other ingredients. The polyol and polyisocyanate react exothermically (generating heat) to form the polymeric structure of the foam matrix. By varying the type and amount of reactants and optional additives, a wide variety of foams can be produced having densities ranging from less than one to over 60 lb/ft3.
The polyol may be either a polyether or a polyester, with polyether polyols used most frequently. The polyisocyanates used most often in the production of rigid urethane foams are TDI (tolylene diisocyanate) and preferably, MDI (diphenylmethane diisocyanate). A polymeric form of MDI (crude MDI) is often used.
Polyurethane foams are usually prepared by the prepolymer process and preferably by the one-shot process. The reactants, prepolymers containing isocyanate groups or polyisocyanates, and polyols, together with blowing agents and catalysts, optionally with assistants and additives, are fed in metered amounts, separately or in the form of mixtures, to a mixing device, e.g., a mixing head, where they are thoroughly mixed and poured from dispensing devices, into molds or into cavities which are to be filled, and within which the mixture foams and cures.
It is also known to manufacture polyurethane foams from two-component systems, where component xe2x80x9cAxe2x80x9d preferably contains the organic polyol, the catalyst, blowing agents and additives and component xe2x80x9cBxe2x80x9d consists of polyisocyanates, with or without further assistants. The two components are separately stored in multi-compartment containers, preferably two-compartment containers. Before processing, the partition between the two compartments is destroyed and components xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d are mixed, after which the foamable mixture is processed.
It is additionally known that components xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d can be separately introduced into aerosol cans, stored, mixed by means of a suitable device and discharged from the can as a foamable mixture. A disadvantage of the process described is that it uses an expensive multi-compartment container with a mixing device, and that the entire contents of the can must be processed at once, since the mixture of components xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d cannot be stored.
U.S. Pat. No. 3,830,760 describes the manufacture of foamable polyurethane mixtures. Mixtures of the curable polymer or polymer intermediate and an inert blowing agent which is soluble in the polymer are accommodated in a container from which any desired amount of foam, within the limit of the capacity of the container, can be dispensed. Though the one-component foam allows convenient and advantageous processing, for example, it can be discharged from the aerosol can without weighing and mixing, this process also has certain disadvantages. For example the polyurethane mixture described in U.S. Pat. No. 3,830,760 has only a limited shelf life, the viscosity of the mixture rises relatively rapidly, and the contents can solidify on prolonged storage. It is a further disadvantage that the foamed polyurethane mixture reacts with the atmosphere, and cures, relatively slowly, so that the polyurethane foam may undergo post-expansion. This can lead to distortion of articles which have been filled with foam, for example, door frames or window frames.
U.S. Pat. No. 4,258,140 solves the post-expansion problem by releasing, and curing by interaction with the atmosphere, preferably with atmospheric moisture, a storage-stable mixture, which is under pressure, of prepolymers which contain isocyanate groups and are based on polyols and organic polyisocyanates, and blowing agents, with or without assistants and additives, wherein the polyols used are difunctional to octafunctional polyester-polyols and/or polyether-polyols which have an hydroxyl number of from 40 to 500 and contain chemically bonded tertiary amino groups in the polymer chain, or mixtures of such polyester-polyols and/or polyether-polyols, containing tertiary amino groups with nitrogen-free polyester-polyols and/or polyester-polyols. The foamable mixtures are expressly indicated to not contain any conventional low molecular weight monomeric polyurethane catalysts, for example, catalysts with molecular weights of less than 300, such as tertiary amines, salts of organic acids, organic tin compounds, and the like.
Commercially available one-component foams are not designed for the combination of low pressure build and dimensional integrity. Competitive one-component foams generally exhibit pressure builds within the range of 2 to 8 psig. One commercially available product manufactured by Hilti, and sold under the tradename CF 116 Filler Foam or CF 128 Insulating Foam, both products being single-component polyurethane based foams, the CF 128 product additionally being CFC-Free, does result in low pressure build up, but fails in dimensional stability as measured in direct comparison with the compositions of this invention.
It is an object of this invention to overcome the limitations of the prior art and to provide a one-component, at least semi-rigid, essentially closed cell polyurethane foam that cures upon exposure to atmospheric moisture, yet retains dimensional stability and results in low pressure build up within a cavity.
It is another object of this invention to provide a polyurethane foam that uses conventional catalysts.
These and other objects of this invention will be evident when viewed in light of the drawings, detailed description, and appended claims.